Not Applicable
This invention relates in general to opposed antifricton bearings and more particularly to a process for setting such bearings in preload and for verifying the force preload.
One can find rotating shafts in a wide variety of machinery, and when such shafts carry heavy loads or must rotate with a good measure of precision, they are often supported on antifricton bearings. Usually the antifriction bearings arranged in a pair, with the bearings of the pair being adjusted against each other to a desired setting. Typical of the bearings are single row tapered roller bearings. When positioned with the large ends of the tapered rollers in the two bearings presented away from each other (indirect mounting) or the large ends of the rollers presented toward each other (direct mounting), displacement of one race of one of the bearing axially will change the setting for the two bearings.
Where the axis of rotation must remain perfectly stable, such as in the pinion assemblies for automotive differentials or in machine tool spindles, the bearings that support the rotating components should operate in a condition of preload, which is characterized by an absence of clearances, both axial and radial, in the bearings. Typically, preload, like end play where clearances exist, is considered in the context of an axial dimension (e.g. 0.002 in. preload), but the real and more meaningful measure of preload is in the context of the internal forces captured by the opposed bearings. In this regard, several pairs of bearings identical in size and configuration, all set to the same dimensional preload could well lock in different internal forces, that is to say, different force preloads. Pinion assemblies for automotive differentials illustrate the problems and uncertainties one encounters in connection with setting the bearings. The typical pinion assembly has a carrier, a pinion shaft provided with a pinion at its one end, and a pair of tapered roller bearings which support the shaft in the carrier. When the carrier is attached to the main housing of a differential, the pinion meshes with a ring gear, and to insure that the mesh is proper, the bearings must be set to preload.
Typically, the procedure for adjusting the bearings in a pinion assembly involves fitting the shaft to the carrier with one of the tapered rollers of the bearing seated along the raceways for that bearing. Thereupon, measurements are taken from the other bearing to determine the size of a spacer, which, when installed, will impart the proper preload to the two bearings. The assembly procedure is then completed using the spacer. Thereafter, the torque required to rotate the shaft is measured to see if it falls within acceptable limits. But torque does not provide a very good measure of preload, because in identical pinion assemblies set to the same force preload, torque can vary as much as xc2x120%. In view of this variance, some pinion assemblies which exhibit torque outside the accepted range may actually have an acceptable force preload. This can lead to expensive disassembly and reassembly. Then again, some that exhibit a torque within the acceptable range may actually have an unacceptable force preload. And too much force preload can lead to early failure of the bearings. On the other hand, too little force preload may permit excursions into end play owing to differential thermal expansions between the carrier and shaft during operation. End play detracts for the stability of the pinion shaft and may allow the pinion to assume positions which lead to wear and create annoying noise.
The present invention resides in a process for setting opposed antifriction bearings with a desired dimensional preload and verifying that the force preload is acceptable. To this end, machine components are assembled with one of the bearings in place between them. The other bearing has a gauge interposed in it and the gauge provides measurement for determining the size of a spacer which will give the bearings a desired dimensional preload. The gauge also exerts a known axial force on the bearings, and while that force is exerted the torque required by the bearings is measured. This provides a torque signature. When the other bearing is assembled without the gauge and with the spacer installed to provide the desired dimensional preload, the torque is again measured, and from this new torque and the torque signature, one can determine the load, that is the force preload, in the bearings.